1. Field of the Invention
The present invention relates to a shaving cutter for use in finish cutting of gears.
2. Description of the Prior Art
It is a common measure to use a shaving cutter in finishing the surface of a gear which has been produced by a gear cutting by generation process or the like method, in order to trim the profile of the gear teeth and to improve the fineness of the gear surface.
FIGS. 1 to 3 show a conventional shaving cutter which is used most popularly. As will be seen from these Figures, this shaving cutter has a form of a spur gear each teeth 2 of which is provided with cutting grooves 3 formed in its surfaces.
This shaving gear has been produced conventionally by a process having the following steps of cutting a metal blank by a gear cutting by generation process or the like method into a shape of a spiral or a spur gear, and cutting a plurality of cutting grooves 3 in the surface of each teeth along the involute curve of the teeth surface. It is extremely difficult to form a large number of cutting grooves 3 intermittently on the surfaces of a large number of teeth 2. The difficulty is enhanced because the cutting grooves 3 have to be formed along the involute curve of each teeth 2. This process, therefore, requires a considerably long time, which constitutes one of the major reasons of the raised price of the shaving cutter. When the shaving cutter has become dull, the involute surfaces of the teeth have to be ground highly precisely, employing a specific involute surface grinder having a high precision. At the present stage, the shaving cutter is applicable only to gears having modules of 16 or lower, and the gears having larger modules cannot be finished with the gear type shaving cutter.
In the use of this type of shaving cutter, the shaving cutter is meshed with the gear blank 4 at a certain inclination. As the shaving cutter is rotated, a slip is caused between the cutter 1 and the surface of teeth of the gear blank 4 to provide a grinding effect on the surfaces of gear teeth of the gear blank 4. With this shaving cutter, only a low cutting efficiency is obtained, because there is a practical limit in the amount of slip between the surfaces of teeth.
In this connection, screw type shaving cutters which have been used also conventionally can provide higher cutting efficiency because this type of shaving cutter can cause a larger slip than that caused by the gear type shaving cutter. In addition, the screw type shaving cutter can be applied to gears having larger modules to effect the finishing by shaving. For this reason, in some cases, a shaving hob 5 constituted by a worm shaft provided with radial cutting grooves 14 has been used for precisely finishing the worm gear. This shaving hob is produced by intermittently rotating a screw-like blank and grooving the blank in the radial direction to form cutting grooves while the blank is kept stationary. After the cutting of one groove, the blank is rotated and indexed for the cutting of next groove. Then, after a further indexing, a further cutting groove is formed. The work is thus made intermittently taking a long time at an extremely low efficiency of the work, resulting in a raised price of the shaving hob.
Although it has been known that the precision of the gear and the finess of the gear surface are improved by a finishing with the shaving hob 5, the use of the shaving hob has not been spread because of the difficulty in the production.
More specifically, in a shaving hob 5 having radial cutting edges 15, each cutting edge 15 cuts an area shown by a one-dot-and-dash line. As the hob 15 is rotated, the cutting edge 15 occupies the positions 1 , 2 , 3 , 4 relatively to the teeth surface. The cutting of the gear teeth surface by the cutting edge 15 is liable to incur a vibration in the rotational direction of the gear and in the axial direction of the hob 15. The movement in the period between the operation of a cutting edge and the operation of a next cutting edge is rendered not uniform. Thus, with this type of shaving hob cannot provide a sufficient improvement of the fineness of the tooth surface and improvement of the precision of the tooth profile.